How to Choose a Refrigerator

Your refrigerator could be the largest consumer of electricity in your off the grid home. Selecting the right one for you is less about aesthetics and more about size versus power usage.

Less than two decades ago it made sense to purchase a propane refrigerator for two reasons:

Solar electricity was prohibitively expensive

AC power inverters were expensive, inefficient and most made a poor quality electricity such as the infamous modified sine wave.

There were many propane choices such as Danby, Servel and Dometic. Dometic was a common choice as they make smaller and rugged fridges designed for the RV and marine industries.

The downside of the propane fridge is the cost. They are expensive to purchase and operate. Expect to pay up to $2500 initially and $15 to $30 per month for the operation of your propane fridge. If you only use it for a few months in the summer, this extra cost is insignificant. However year round use is expensive and inconvenient.

As solar energy became a bit more affordable the DC fridge gained some traction. The common recommended DC refrigerators were the Sunfrost from Arcata California. These fridges are high end, 12 or 24 volt, and very efficient. When you added the 25% or so gained by not using a modified sine wave inverter, they were and are a good choice. The downside is they are made one at a time and are priced from $1500-$3000 and even higher. They must be crated and shipped by truck which can easily add another $500-$1000 to the total cost. If something were to go wrong like a compressor burning out, repairs are very difficult. No one stocks parts for these beautiful machines and no one seems to know how to repair them, although they don’t operate any differently than a 120 volt version. If you can afford one, we still highly recommend the Sunfrost refrigerators and freezers.

Now that solar is more affordable and inverters are much more efficient the “off the shelf” refrigerator is probably the best solution for most of us.

For the average off grid homestead, a good quality off the shelf fridge is the answer. You should be able to go to your local Sears or Home Depot and find a refrigerator/freezer that consumes about 1 kWh per day. That is definitely within the range a solar home can handle.

Types of Refrigerator Cooling Systems

Fridges are usually cooled by one of three methods:

The condenser is a series of pipes or fins on the back of the fridge.

The condenser is located on the rear or on the bottom of the fridge and it looks like a car radiator or car air conditioning condenser. This small radiator like device is cooled by a fan.

There is no compressor. The fridge is cooled via a heating element that drives the cooling system via absorption.

We prefer the second type as there are options for making the fridge more efficient by adding some duct work to the outside or a cool area of your home. By doing this you can supply cold air to the condenser instead of the hot air surrounding the fridge.

The #3 type absorption fridge is never efficient. It is essentially an electric heating element that uses a lot of electricity. This type of refrigerator has been reserved for the RV and marine industry but now can be found in some hotels and conference centers. We are not sure why anyone would use one other than they are very quiet and have no moving mechanical parts.

If you find two fridges that are relatively the same as far as size and efficiency but are cooled by different methods as above, buy type number 2.

Choosing a Refrigerator (“Off the Shelf”) Considerations

The most efficient type of refrigerator is the fridge only model. These are quite rare and not likely what you will want, but they are still worth mentioning.

The most efficient fridge/freezer is the freezer on top. Cold air is heavy and falls from the freezer chamber to the fridge using no fan or pump. The bottom freezer model all use electricity to move the cold freezer air up to the fridge compartment. The side by side models are usually not that efficient either and are best avoided.

Ice makers consume too much electricity. Do not buy a fridge with an automatic ice maker. You can spend a few minutes a month filling the ice cube tray.

Do not buy a fridge with auto defrost. These refrigerators use a timer and electrical heating elements that consume a huge amount of electricity every so many days. This can add many kWhs per year of operating electricity. The second problem with auto defrost is the timers/computers can be confused by generators or poor quality sine waves making the auto defrost cycle happen more than normal.

Do not use a new fridge with a modified sine wave inverter. Today’s refrigerators use fancy electronics and computers for temperature regulation. It is not uncommon for a new fridge to be completely destroyed in a short time by a poor quality sine wave.

Only purchase the size of fridge that you NEED. An 18 cubic foot or so should be plenty for the average family of 5 or 6. A large fridge with empty space will waste energy.

Do not purchase a fridge with condensation control or anti sweat system. As refrigerator manufacturers have realized that condensation on the outside of a fridge might bother a consumer they have added heating elements to prevent it. Rather than insulating the refrigerator better, (which would eliminate condensation) they add electric elements on the outside panels of the doors and sides. These elements operate 24 hours per day or just when they sense humidity. This is not what you want if you are trying to save energy. If you get stuck with this type of fridge turn it off via the “energy saving switch” or cut the wires.

How to Purchase the Most Efficient Refrigerator?

It might seem too easy but the best way to buy an efficient fridge is by locating one without all the bells and whistles and looking at the “Energy Guide” label or documentation.

We are not talking about Energy Star or some other sort of bogus certification.

Simply look at the label that states how many kWh per year the fridge will use. You should be able to find an 18 to 20 cubic foot unit with an energy consumption of under 365 kWh per year. If you keep to this standard you will be able to operate your fridge with about 1000 watts of solar modules, even in the worst of climates.

Thanks for this informative piece! Would you be able to comment on my plans.? I’m planning to install two 100 watt Vikram panels, a Morningstar PS-15 controller, and two Trojan T-105 6 volt golf cart batteries in series (225 amp hours). My location gets about 4.2 sun hours a day. I’m doing all this in hopes of powering a small 3.6 cu ft. Norcold AC/DC fridge that has a 5.5 amp draw (68 watts?). I only use my cabin on weekends from May thru October. I plan on putting the batteries in an insulated, vented box inside a very small unheated shed on the sunny side of the cabin (it’s already there). The fridge is the ONLY thing I would be connecting to the batteries. Will this work, and can I go up a bit in cu ft? Thank you!! (I’m stressing about this!)

P.S. I’m actually getting the new Norcold for free, otherwise I’d probably go with a different brand.

Thank you so much for writing to me. I appreciate it! Your 200 watts of solar should provide about 630 watt hours or .63kWh of electricity (200 watts X 4.2 hours – 25% = 630 watt hours) per day on average. I subtracted the 25% as solar modules do not produce their full output..ever…even with MPPT controllers.

Refrigerator compressors usually operate about 8 hours per day depending on ambient temperature, how often the door is opened, how clean the fridge’s cooling equipment is and how much ventilation the fridge gets. When we multiply 68 watts X 8 hours we get a daily requirement of 544 watt hours or .544 kWh. That is tight as far as producing enough power to operate the fridge.

Now the battery bank. You hypothetically have 2700 watt hours (6 volts X 225AH X 2 batteries) of storage in your battery bank if you discharge them to 100%. At a 50% discharge you have 1350 watt hours of battery storage or about 2 days of fridge operation. That is tight as well as I am assuming you can have more than 2 days of rainy weather at a time.

My thoughts are that this setup will constantly be starving for electricity. There is just not enough margin.

Imagine now you have had 2 days of no sun, your batteries are 50% discharged but the good news is the weather will be sunny for the next few days. Now the solar modules need to operate the fridge plus somehow bring the batteries back to a full state of charge.

If the fridge uses 544WH per day and your solar modules produce 630WH per day, you only have 86WH extra per day to try to bring the batteries back to a full state of charge. It would take weeks to recharge the batteries at that rate.

If you are planning on only having the fridge turned on while you are there on the weekend and the occasional week or two, your system will work flawlessly.

What are your thoughts? I hope I am not being discouraging. I just want you to have success…Jody

Hi Jody,
Thank you so much! Not at all discouraging. It’s very helpful. It sounds like, if I increase the panel wattage to 300 total (two 150W panels) and go with a fridge that has a lower amp draw (maybe 3.5), I can do much better and not have such a starved system. That would actually give me a little over 600WH/day extra. I’m assuming I could still stay with the two battery configuration.
Does that sound more doable?

Your last statement is true- I would only be using the fridge on the weekends, and probably only 1-2 times each month during the May-Oct. timeframe.

Sorry for the delay. Increasing the solar output is a great idea as well as getting a more efficient fridge. You will need a bigger charge controller; MPPT if possible.

If you are only going to operate the fridge on weekends and the occasional week, 2 batteries should be enough. If you want to leave the fridge on all the time, 4 T105s would be the solution. Great work…Jody

If this is only a weekend cabin if you could afford it I would try and get 4 batteries by the time they charged all week you’ll have a lot more power,,, that way you could possibly charge a laptop or a cell phone,,,, entertainment needs ,,,,DC powered LED lighting would be a plus especially in a remote area cabin like that,,,,, even though it’s just a weekend cabin you may find yourself in a situation where you want to spend an extra day or two those extra two batteries would really help,,,,,I’m not sure about your choice of a charge controller I have a PS 30m metered version Morningstar pwm charge controller works like a charm,,,,,however I boxed it up and put it away in favor of an mppt charge controller they wring out your panels and get as much as they possibly can out of the Sun,,,and panels,,,,you being limited on sun 4.2 hours I believe you said something along those lines,,,,, you may want to look at an mppt charge controller,,,,you could look at Amazon and see what people are buying and how they’re reviewing it,,,, as far as the refrigerator I don’t have any experience with that particular model and I don’t think I’ve read too much on that particular model either,,,,, I do know there are some really good DC powered refrigerators out there however they are somewhat cost-prohibitive for some of us,,,,ARB,,,Engle,,, are very efficient and will probably use the least amount of power the nor cold I don’t know what they run or how efficient the are,,,,,you might want to read up on some reviews of your particular model say like on Amazon,,,,, or just Google reviews of that model find out how much power it’s using,,,,if it’s keeping things cold enough,,,,, I know for the money Wynter makes a pretty nice one ,,, it runs on DC power and gets top reviews among its many owners some of the more costly ones I believe actually have a freezer and a refrigerator compartment all in the same unit,,,,,arb,,,,Engle,,, will probably last the longest and use the least amount of power however for the money whynter does get top reviews,,, and try and remember 200 Watts sounds like a lot ,,,, it may be perfect for one and a half,,,, two days,,,, at a cabin butt if you stay longer the batteries most likely will have trouble recovering in time from two 100 watt panels,,,,, however if you’re charge 4 Batteries all week with a good charge controller a full 5 days to charge,,,, and you’re only going to stay the weekend,,,,with four batteries I think you’d probably be ok.renorgy panels are relatively inexpensive work really great last a long time have a good warranty,,,, I use them and I’ve had no complaints so far,,, they also sell a bunch of other stuff that might be of interest to anyone doing a cabin you can find a lot of their stuff on Amazon.

Thank you! I don’t know if this reply will get to you. I replied to Jody yesterday, but I don’t see my reply posted.
In any event, it sounds like I should increase my wattage on the panels and find a fridge with a lower amp draw. Secondly, I may have to go with 4 batteries in series and consider an moot controller (which is less $ than I expected). But aren’t the y better suited for larger arrays?

As your system is 12 volts, you will need at least a 25 amp charge controller (MPPT preferable) with 300 watts of PV.

The batteries depend on what you can afford. You could always try your system with 2 batteries and add two more in a month or two if things aren’t working out. Just don’t mix batteries of more than about 6 months difference in age. The 6 months is not written in stone. Their are differing opinions. But we all agree the closer the batteries are in age (and amount of usage), the better your battery bank will perform.

When you buy your batteries look at the manufacture date of each battery. I have seen batteries sold as new that were over two years old as they sat on the dealer’s shelf a long time.
Jody

Thank you Jody and Bear Cat for the helpful information. I think I know now what I need to do!
One other question, if I may…. Because I don’t use the cabin during the winter months, I’ll have to transport the batteries home for the winter. I have a heated garage. Is it possible to hook these batteries, connected in series, to a trickle charger during the winter until I bring them back to the cabin in the spring? Thanks!

An mppt charge controller is a really good way to go with a small or a large system in my own personal opinion ,,,a PWM charge controller is great I used one for about a year It worked pretty good however they just can’t pull everything that’s available out of your panels and put it in your batterys An mppt charge controller will take in all Power it can through the panels and put it into your power pack it does a pretty good job on cloudy overcast days when sunlight is very limited ,,,my tracer 4210 also has what they call solar boost it’s always trying to give you a little bit extra then whats actually coming in ,,,also the 4210 is rated at 500 watts for 12 volts/1000watts for 24 volts not the very best charge controller in the world however for the money I’ve been pretty impressed with it so far if you check the reviews on Amazon you’ll find that most of the owners really like it and have had really good luck with it

Hello Jody, Thank you so much for the great information. I only wish I had found this post 9 months ago when I was putting a system together and stressed out about my calculations. I would really appreciate your opinion on our system.
We have a cottage off the coast of Maine which is in use for May-September. I have installed four 285 watt panels due south running two pairs of panels in series with 4awg 85′ copper to the load center. A midnite solar classic is charging four Fullriver L16 (415a@20c) AGM batteries. A pure Sine Magnum MS4024 inverter has a half dozen LED lights and a soon to be purchased refrigerator on it. According to the charge controller, the panels are putting out about 950w at noon on a clear June 21st day!
Questions: Do you think I have enough battery reserve for a 339kWh “inverter” refrigerator?
What do you think of the new “inverter” refrigerators coming out on the general market? they claim to be more efficient and quieter by running the compressor at variable speeds instead of hard cycling.
We are looking at the LG LTNC11121V if anyone out there has an opinion.
Jason

Sorry for the delay. I have been sick the past few days. Since you are only using your cottage from May to September, that certainly simplifies things. You have hard winters and very little sun making a completely independent solar system (in winter) difficult. Also as it is a cottage I am going to assume you are using it mostly on weekends with maybe the occasional week or two week stay during the summer. If I am wrong let me know.

As you are using 4 AGM L16s you have about 5 kWh of storage at 50% discharge. Your fridge requires a little less than a kilowatt hour of power per day (likely closer to a kWh as your usage is during the hottest part of the year when the fridge will work the hardest). If nothing else was turned on, you would have five full days of storage (down to 50% discharge) assuming no sun for that period. That should be plenty if this is a weekend cottage as it will charge up thru the week and be discharged over the weekend.

If this is a seven day a week cottage, I would likely still not change anything. Your solar array is a good size to operate the fridge and your LEDs however you will most likely find yourself collecting more electrical appliances as the years go by. That is the beauty of solar. You can always add more modules as needed. You have the best charge controller on planet earth and assuming you bought the Classic 150 you can double your solar array without buying a new controller.

I see nothing wrong with the inverter/variable speed compressors. They do tend to operate a lot more in a 24 hour period but they use less electricity per hour making them reasonably efficient. As they have auto defrost they are using more electricity for that heating element. They also have a much more complicated operating system (computer controls and inverter compressor) than a typical fridge making more to go wrong with these than a typical fridge/freezer combo. If the fridge is always powered by your MS4024 everything will be fine. However if you plan to charge the batteries at times from a standard 120/240 volt generator, I would stay away from the inverter compressor units as the generator’s electricity will not be near as clean as the MS4024 which could mess with the LG’s computer and interfere with the auto defrost system. The last negative with the model you are looking at is the auto ice maker. If having ice all the time is a priority for you, then the extra power consumption is worth it. If not, it is likely you can find a more efficient fridge of the same size.

We use an 18 cubic foot “off the shelf” fridge/freezer that uses less than 1 kilowatt hour per day. That is another 7 cubic feet with a tiny more energy consumption. I assume that can be explained by the lack of auto defrost and ice maker.

I am not trying to put down the fridge you are using. It looks like a beautiful machine. With the system you have designed, your fridge will work great for you.

You really have done a great job with this. One last thing I would mention with you being on the coast in Maine. Usually we would tilt or modules at the Latitude and point them at solar south. However if you find you have fog first thing in the morning, it might make sense to aim the modules more south west to collect solar after the fog has burned off. Depending on where you are, you may or may not have to account for this. Great work Jason…Jody

Thank You! We really appreciate your comments. The cottage is used continually during the summer but I have taken measures like mechanical timers on certain lights and outlets for charging mobile devices to keep energy use down. I like your comment about morning fog and will expand on the west roof when the time comes. We have not yet purchased the refrigerator yet but our trusty propane fridge is getting cranky so we need to act soon. I like the “inverter” models because of there advertised quiet operation but I agree with you that simpler is always better for appliances. Problematic generator operation is a real concern. The funny thing about the ice maker on this frig is that it looks automatic but is really fancy knobs that manually turn the trays 🙂
We would love to get responses from the community on models that have worked well for folks in our situation. Nobody specifies operational sound levels and I don’t want to pine for the good old days of the silence of propane as I am trying to ignore a loud compressor.

Lots to add but the most counterintuitive is to use a freezer modified to refrigerator temps. Very cheap, very efficient but a top loader….which could be worked into a counter. Plus – we use a regular freezer as freezer in the summer when we have much more solar power and we don’t use it in the winter at all because it is cold outside. Our food shed is separate from the house so it can get cold.

Good to hear from you. You are correct. I need to learn more about freezer/fridge conversion for those who are happy with a chest fridge. Like you say it could double as counter space. Great idea! We have an 18 cubic foot fridge/freezer (freezer on top) from Sears and it consumes about 1 kWh per day on average. It has no auto defrost which adds to its low power usage. We also have a 20 cubic foot upright freezer as we are a family of seven. It is likely the worst freezer I could have but when funds are tight you do what you have to do. We need it year round as we buy meat in bulk from local organic (sort of) farmers and need the storage. It is stored in an uninsulated garage so it hardly operates in the winter…thankfully.

You have the right idea. Use the freezer in the summer when power is plentiful but store it for the winter when solar power is hard to come by. If you want to send me a copy of your book, I will write a full page review with a link back to your website. We need to support each other as solar pioneers as much as we can as we are few and far between. We are working on some very specific books on topics like “How to Make Your Battery Bank Last as Long as Possible” or “Choosing appliances for your off the grid home” and things like that. I could write a 1000 page book on how to design, source the parts, install and maintain your renewable energy system but it is information overload for most folks who will never take the plunge off off grid living anyway. I wrote a short book on Amazon (re: Saving Energy) about 5 years ago and it sells maybe 5 copies a month. Not so hot.

Keep up your great work David and if there is anything I can do for you please do not hesitate to ask…Jody

I’ll send you a copy. Thanks. We are selling quite a few, actually. About 5 a day. Word of mouth only. Having said that, it is only because it is funny. I screw up so much I can fill several books. People seem to like the uber fallibility I bring to the subject. They don’t learn anything except maybe a bit of first aid.
Funny you should say what you did…..I know you know your stuff. And some readers dis ask for more info and I did refer them….but…maybe….we should collaborate? Your knowledge and my self destructive style? Maybe not. I’ll leave it with you.
I just installed my third set of batteries in 12 years. The first set, I murdered, tortured, neglected and eventually chopped the heads off! I now wear a black headress. The second set (three banks of 4 x 12volts), I kept going for 7.5 years. I had 600 ah of 8D’s at 48 volts. Now I have 430 ah of Discover 12v.
BUT!! Quel surprise! Taking the first four out of the old line up revealed a sore loser and so I tried re-cobbling 2/3 of the old ‘line’ (eight batteries from the original 7.5 year old string of 12 x 8D’s) and I put ’em on a separate ‘switched’ line. NOW I am getting good readings on the old and the new. 800 amphours!!

Thanks David,
Selling 5 books a day is amazing. Especially in Canada. Good work. Its funny you mention mistakes as I have ruined more inverters and charge controllers than most have ever laid eyes on. Batteries are another story. That is why I highly recommend folks start with a cheaper set of batteries for their first set and then once they have ruined them, buy a better set. We all do it. I would definitely collaborate with you. I have read your info and know you have more experience than most. Anything I can do to help I will do my best. I spend a fair amount of time in Haiti and have just recently began training Zimbabwean installers how to install solar in rural Zimbabwe, Zambia and South Africa so my time is limited but I will catch up at some point. I think there is a link at the top of our website to show our efforts in Zimbabwe but I am not sure if I’ve got that done yet. I am running in ten directions all the time. Your work is impressive. Keep it up. Love to read and recommend your book…Jody

Chest freezer conversions are not all they’re cracked up to be you can save on energy to an extent,,,, however there are things that need to be considered there’s condensation issues sometimes exterior condensation and interior that could be quite a pain you’ll have to invest in a small fan that will circulate air inside of that chest freezer or you’ll end up with 38 degrees down toward the bottom and 55 degrees or more for things at the top and again the moisture issues especially in the summertime if you live in the area that gets high humidity in the summer like I do the humidity would just be ridiculous everything would be swimming around in inside literally so much water from the condensation and then you also have to ask yourself do you need a freezer if you do you just cancelled your savings completely out by rigging up the chest job,,,,, if you have to pay to run the freezer also,,,,, then you have to turn around and run the refrigerator,,,,, if you don’t want to run a small DC powered refrigerator my advice would be just to get enough battery and enough solar and a good charge controller to run a regular small top freezer refrigerator 16 to 18 cubic foot, ,, I run an 18 cubic foot Frigidaire top freezer,,,,, I have adequate freezer space and I have plenty room in the refrigerator,,, I really don’t feel that I’m missing out on anything ,,,,which you will if you use a deep freezer because all you’re going to have is a wet refrigerator that has wide temperature fluctuation wide temperature swing,,,, if you want to work through all those issues and you don’t need a freezer then the chest freezer conversion could be for you if you don’t mind the pain of having to deal with all the condensation however. It would be more costly however if you wanted to use a chest type configuration I would look at Sundanzer or,,,steca,,, I believe you can find these units for sale on Amazon and quite possibly a few other places they’ll work on DC power so you don’t have to invert,,,, all in all though if you really sit down and look at it you’ll end up saving money if you buy somewheres between 800 and 1000 Watts worth of solar,,,, 24 volt configuration,,, 12 volt configuration,,, whatever you decide works best for you,,, 4,,,L 16 batterys would be best,,,, if you can’t afford that try to go with 4 ,,,, Trojan t105 or their equivalency,,,, this should work out rather well in most areas,,, and if you can afford the serious coinage you may look at rolls surret they’re probably among the very best

Thanks so much for your comments. As I have no first hand experience I would like to hear from others and their experiences with “CHEST FREEZERS AS REFRIGERATORS”. I have heard they are awesome and heard they are disappointing…

I would like a complete list of available solar/ off grid/ marine appliances . We are undertaking a grand project with 27 acres, we plan to have solar /wind turbines, ect. so we will be looking for and buying only these types of goods for our undertakings. Please include pricing as that will most determine the funding aspects of our choices
, without it, we will look elsewhere.

Thank you for your comment. Unfortunately there is not a magical list of all items of all manufacturers with pricing. You have provided no information about your grand undertaking making it impossible for me to answer your questions. I think it would be best for you to look elsewhere as noted in your comment. I wish you the best in your renewable energy adventures. If I can ever be of assistance please let me know…Jody

I want to purchase a refrigerator/freezer for my RV around 7 ft3. I have 200w of solar panel and a 2000w pure sine inverter. I do not want the typical RV unit from Dometic or Norcold! Do you have any suggestions?

You are making a good decision by avoiding those brand names as the are made for looks and using propane, not for being energy efficient, especially when using 12 volts DC or 120 volts AC. Any off-the-shelf small refrigerator would be perfect for your application. Just look at the energy consumption as stated on the unit or on a sticker or card fastened to the unit and find the fridge that uses the least amount of kWhs per year. You should be able to find a fridge that small that uses about 180 kWhs per year or 0.5 kWhs per day. Take care…Jody

Don’t try to invert power for a small solar setup to run a refrigerator buy a wynter from Walmart or Amazon or just go to Amazon and look at the ARB and the Engle wynter ,,,dometic refrigerators they work off of pure DC power either 12 or 24 volts and you can get them from 45 quarts up to probably 80 or 90 quarts which is pretty big when you really stop and think about it and they work off of DC power without having to invert,,,, to run a full size refrigerator you’re going to need between 800 and 1,000 watts of power and 4/6 volt heavy duty golf cart batteries,,,, some of these refrigerators that run on DC are very costly however the wynter 45 quart model could be purchased for about $450 sometimes slightly less and those that owned it has pretty good reviews to say about it overall there are bigger things available that cost even more ,,,,Sundancer,,,, stecca,,,, just to name a few they run on DC power

The Whynter FM-45G 45 Quart Portable Refrigerator can be a great option for some. The quality is excellent; they are a compressor based DC fridge/freezer but 45 quarts is only 1 3/4 cubic feet. We have a family of six making a 1.75 cubic foot fridge or freezer of no use for us but I am sure some would be very happy with such a small efficient unit.

I’m new to all this too I’m learning here ,,,,,sometimes I just offer what I’ve done not really so much as personal advice but just as a reference as to how Ive done it everybody has different needs,,,,, one thing I personally have found if you are run a full size refrigerator stay away from modified sine wave I had an older Whirlpool freezer on top mechanical controls nothing digital,,, I pretty much ruined that refrigerator course it was getting older it was over 10 years old but just running it six or seven months or so on modified sine wave I pretty much ruined it,,,, doesn’t work anymore stay away from that get a pure sine wave I got a real nice one off from Amazon they have all kinds of them to choose from read the ratings and see who’s buying what and what kind of success they’re having with it,,,, I run an 18 cubic foot Frigidaire off of my 1500 watt inverter I have 800 watts I’m going to soon have a thousand watts when I install two more panels however I did not parallel 800 watts together on one charge controller I believe that that’s a lot of amps to try and deal with and might not be a hundred percent safe ,,,,,other people will argue that and say it’s very manageable and they could be right,,,,idk,,, what I did was took 2 renorgy actually Tracer sold by renergy 4210 mppt charge controllers I put 4 100 watt 12 volt panels on each one they’re good for up to 5 100 watt panels @ 12 volts,,,,,1000,,,,@ 24 volts and I plan on putting 5 on each one in the near future,,,, everything’s grounded and fused myself personally I’m using 8 AWG wire in conduit,,,, so I have two parallel systems hitting the same battery pack if you have 4 good heavy duty 6 volt golf cart batteries with a system like this you should be able to do really good job running a refrigerator ,,,,if you need the extra power for winter time and cloudy overcast days I also have an Iota DLS battery charger again you can find on Amazon,,,, I can hook up to my Eu 2000 Honda inverter generator and charge my battery pack that way if I have a lot of bad weather and that happens ,,,,that’s something to consider sorry so long-winded but I see a lot of people worry so very much for trying to run a refrigerator on solar,,,, such as I did when I started,,, and I made some mistakes however through trial and error I believe 800/1000 watts is the magic numbers,,,, course that depends on where you live and what you’re running what your weather is like,,,,,however as a rule of thumb that work pretty good you can always build a smaller system or system about that size to deal with your entertainment needs tv’s radio laptop charging things of this nature and Amazon sells LED lights complete with cabling and socket and bulb for I think $14 somewhere in that ballpark and they’re DC power so you will not have to invert to run them.

Thank you for your comments. We are all new to this. Renewable energy is such a young industry there are not a lot of real experts in the field. Someone who has read a few books and has a certificate is not necessarily the best person to seek advice from. It is from folks who have experience that the most can be learned.

I completely agree with you regarding modified sine wave inverters. They destroy motors, electronics, batteries, battery chargers, laptop batteries and the list goes on and on. Most modern refrigerators will not even operate with anything but a sine wave inverter. When I started in the industry, it was very expensive to buy a real sine wave inverter as there were only two decent manufacturers and they were made in small volumes. But since Trace’s introduction of the SW series (SW4024, SW4048 etc.), real, true, pure sine wave inverters are much more affordable, reliable and a must.

Refrigerators use computers to control temperature and also have high efficiency motors/compressors. These items are either destroyed instantly or within months if you try to use a low quality and inexpensive modified sine wave inverter. Don’t buy one you will regret it!

I didn’t realize you can still get the Iota DLS battery chargers. We have used and had our customers use 100s of these with very little failures. They are an awesome battery charger/RV converter. They produce very stable DC and make a great battery charger. Thanks for that info. I still have a few 24 volt models left over from our solar store and I would hate to part with them as they are such a great unit.

Hello…
I am looking at a Danby 11 sq ft refrigerator freezer to use with my campsite with solar…
I have a 45 watt starter solar kit from Harbor Freight…
If I add a 110 watt solar panel and another battery… Would that be enough to run the fridge???
Thanks,
Art G

Thank you for your comment and question.
I would need more info such as your current battery bank and how much more battery capacity you plan on adding to answer your question accurately.
Danby freezers are very efficient and a great choice for your campsite…Jody

Question
How many panels and battery’s for this fridge to run?Kenmore 60412 18 cu. ft. Top Freezer Refrigerator w/ Wire Shelves – 404.0 kWh per year
I’m in Texas
Lots of sun but also cloudy days n rain
I have a 1800 watt 24 volt system
Not hooked up. Yet

If this is a year round residence and will be operating in the least sunny times of the year we have to size it to work at that time. In the sunnier times of the year, you will just have extra electricity that you can dump, use for things like air conditioning or just let your system disconnect the solar array when the power is not needed.

Your fridge uses 404 kWh per year or 1.107 kWh (or 1107 watt hours) per day so that would be the power required to keep your fridge operating.

In your area, the average amount of sun hours per day is 4.5. That is equivalent to the sun shining on your solar panels at exactly 90 degrees for 4.5 hours per day.

If we take the requirement of 1107 watt hours per day and divide by 4.5 sun hours that gives us a recommended solar array of 246 (250) watts however that is in a perfect world where solar modules produce the maximum output when the sun is shining at a 90 degree angle at 25 degrees Celsius. However they don’t. Even with a high quality MPPT charge controller you will be lucky to get 80% or so. The best plan is to increase your solar array by at least 25% to make sure there is enough power to cover the fridge. Now the solar array would be more like 307-312 watts or the next size up of module or modules added together.

The second consideration is the fact that the sun may not have shown itself for a week. Now your batteries are low. If you only make your solar array large enough to operate the fridge there is nothing left over to bring the batteries back up to a full state of charge.

If this fridge must work (as in a vaccine fridge in Haiti) I would double the size of the solar array however since you are in Texas and likely not operating a hospital I would increase the size of your solar array from the previous calculations by 50%. Now your array would be more like 460-468 watts. Solar modules are cheap (under $1.00 per watt) and there is no excuse anymore for trying to get by on as little as possible (like when we built our first solar off grid system at $16.00 per watt).

It is likely your fridge has an auto defrost cycle which uses electric elements to remove any frost from the inside of your freezer so having that extra solar will be welcome. It would be great if it was manual defrost or you knew how to disable the auto defrost but that is beyond the scope of most folks’ knowledge.

So for the solar array I would recommend two 230-240 watt modules.

Now for the battery bank. One thing we do know when it comes to battery banks is “bigger is better”. The less a battery bank deep cycles the longer it will last.

Every time you remove electricity from a battery and recharge it you have removed life from the battery. If you only take out 10% of the battery’s capacity and recharge, you have only removed a little of the battery’s lifetime. If you take a battery and discharge it completely and then charge it back up you have removed a lot of that battery’s lifetime. The goal is to discharge the battery as little as possible. If you have time read http://solarhomestead.com/battery-amp-hour-ratings/

However money is a factor as well. It would be nice for all of us to be able to spend thousands on a battery bank. But most of us cannot.

Back to your fridge. It consumes 1107 watt hours per day or 43 amp hours per day at 25.6 volts which is a pretty typical battery voltage for a 24 volt bank.

Each T105 or equivalent has a capacity of 225 amp hours at 6 volts or 1350 watt hours if completely discharged from full to nothing left. If you were to put 4 of these in series you would have a 24 volt battery bank at 225 amp hours or 5400 watt hours (5.4 kWh). Now remember that 5400 watts hours is if you completely discharge the battery which we really don’t want to do. But if we did, this battery bank would operate the refrigerator for 4.9 days or 5400 watt hours/1107 watt hours= 4.87. Realistically you would not want to discharge below 50% of the battery bank’s capacity making this battery bank good for about 2 1/2 days.

If you have back up generator this may work for you but a better idea would be to double the battery bank giving you at least 5 days with no sun bringing the battery bank down to 50% or almost 10 days for that weird time when then might not shine for 10 days. Because we made the solar array big enough it will charge the 8 batteries up even from dead in a week or so.

You also need to remember that even on a cloudy day, a well designed solar array will produce 10-40% of its maximum rating. Dark rainy days almost make no power. And no the moon does not charge batteries with solar modules. That is just a joke and there are websites that will you this.

A second option would be 4 units of Trojan’s L16 (370 amp hours at 6 volts=) or equivalent. I only use the brand name Trojan as it is what most are familiar with.

Four L16 batteries would give you a capacity of 8880 watt hours (8.88 kWh) or 8 days bringing the batteries to total deadness (is that a word?) or 4 days to a discharge of 50%.

You’ll have to decide what is best for you. The L16’s are a tougher battery as far as handling deeper discharges but you pay for that extra quality. Golf cart batteries (like the T105) are operating the type of system you are designing all over the world due to their availability and price. I have seen hundreds of them in Haiti and the Dominican, Maine, New Hampshire, Vermont, California, Wisconsin and eastern Canada. Our first battery bank for our home was 16 Trojan T105s and we got 6 years out of them.

When you get your battery bank please take the time to understand all the battery terminology like bulk charge, absorption charge, float charge and equalization charge. Knowing this will help you maintain your battery bank better than 99% of solar homesteaders.

Also, please, please check the electrolyte in all cells of all batteries at least every few months and add DISTILLED water as necessary.

Hope this helps and please don’t hesitate to question anything I have written. I make mistakes all the time…Jody

Thank u very much
OK battery’s I have to use are
114 amp hour 12 volt wired to 24 v
Panels r 24 v
I have 1800 watt panels
They r Walmart
Marine deep cycle maxx two year watrenty
Only thing I can afford
:(..
So how many of these do I need just for fridge ?
Estimate of course
Thank u 🙂
On sunny hot days I will use other things during day only

You are very welcome. What would be the maximum amount of days you could go without any sun? Like I said brightness in the sky will provide power. But what would be the longest it could be a black sky and nothing but rain?

You are pretty limited. I am not familiar with any 48 volt fridges. All of the 12/24 volt fridges are made from the same compressors built in Germany. Assuming you have a sine wave inverter you should look for the most efficient “off the shelf” model you can find. You should be able to get an 18 to 20 cubic foot model that consumes less than 1 kilowatt hour (kWh) per day.

All of the fancy solar fridges like Sunfrost (which are beautiful bhy the way) are only available in 12/24 VDC and 120 VAC. Don’t spend the extra money on a Sunfrost 120 VAC model as they are not that much more efficient than an “off the shelf” model. If it breaks down, who are you going to call to fix it? All the local repair men won’t have a clue how to repair a Sunfrost.

If you don’t have a sine wave inverter you will NEED one for your fridge. Refrigerators do not tolerate modified sine wave (modified square wave) inverters.

i thought i would chime in here with a bit of advice for people running into this sort of issue with trying to run a 12v or 24v appliance or lighting etc.. from a higher voltage system. many times you can tap the center of your battery bank to achieve half of the voltage. i believe you pull the positive from the center and run two negatives to each end of the bank to make sure you are taking power from the bank equally across all batteries. At this point you have essentially two banks of equal voltage one right one left and still have the option of getting full voltage at the end of your string. this is also great for charging a 24volt system with a 12volt source and also using 12 volt lighting on 24volt system as there are many more options at lower prices. this is a new idea to me that i uncovered in researching this issue so make sure to do your due diligence in researching this configuration for your application.

To my knowledge there is no way to tap into a 24 volt battery bank to get 12 volts and draw from it evenly. Sure you can pick a negative in the middle and connect to the end positive to get 12 volts but you will be using half the bank and unbalance the bank causing premature wear on the batteries you are drawing the 12 volts from.

If you draw it out you will see why you cannot just pick a negative in the middle and use it with a positive on one end for one circuit and then connect to the positive on the other end for the other circuit to balance. The other end of the bank will be a negative. There will only be a positive on one end of the bank. The other end of the bank will be a negative providing no voltage and no balance to the battery bank. I will write an article with diagrams as there seems to be a lot of confusion regarding this.

There are four ways to do this:

1. Buy a 24-12 volt DC-DC converter. This is the only proper way to operate a 12 volt appliance with a 24 volt battery bank. However, a DC-DC converter simply changes the 24 volts DC to 24 volts AC. It then reduces the voltage to 12 using a transformer or high frequency switching and then rectifies the 12 volts AC to DC. They are extremely inefficient and fragile and are definitely not something I would use on a reactive load like a refrigerator compressor motor. Motors surge and usually destroy these DC-DC converters quickly.

2. The other option is connecting to one side of the battery bank one one month and connecting to the other side of the battery bank the next month and so on. Doable if you have a lot of free time and you schedule it well.

3. Another option is to make a small 12 volt battery system with solar, wind or microhydro that is exclusively for 12 volt appliances

4. Last option is to buy a 24 volt refrigerator. Problem solved.

None of the options are great and that is why most folks just buy a 120 volt 60hz (or 220-240 50hz) fridge and operate it with an inverter.

I will try to write an article on this as soon as possible…Thanks,Jody

This is a common misunderstanding. When you wire batteries in series to get 24 volts for example, there is not a negative at each end to tap. There is a positive at one end and a negative at the other end. Draw it out or wire a battery bank on the floor.

THIS IS NOT POSSIBLE!

Please do not think this is a solution to operating 12 volt appliances from a 24 volt battery bank or 24 volt appliances from a 48 volt battery bank. It cannot be done!

If you have a 24 volt battery bank you will have to operate 24 volt appliances from it or use the solutions I previously mentioned.

If you don’t believe me, try drawing it or wiring batteries in series, pick the middle positive and then try to find two negatives (one on each end) that will measure 12 volts. They don’t exist. Hope that helps clear things up…Thanks, Jody

Hi Troy, I originally posted to this site before building an off grid home.

In your calcs, you have to also divide the ~1kw/day load of the refrigerator by 24 hours to get the kwh load of the frig. ~1kw per 24hrs /24 hrs = ~40 watts per hour. Which is what I’m seeing consumed by the refrigerator. Note that the refrigerator turns off and on during the day. I have a full size off grid home, and what I’m seeing as Tare (the power required to support the systems that need to run continuously: inverter, refrigerator, fire alarm, etc.) is ~90 watts, and with the refrigerator running, it goes up to ~140w for the time that it is on.

Have you had a chance to do a load profile for the home? It would really give what you need to size the system and do tradeoffs, which could include DC and propane powered refrigerators.

Good thread here. I am doing the design on a tiny home that will ultimately have ten cells at 240 to 300w. Now full disclosure, I work for Polar Power Inc. We make all manner of solar hybrid systems. In talking to my chief electrical engineer about this project he tells me to keep my average electrical consumption to below 5-600w for this system size. It makes sense: On average, there is 6 hours of bright sun and accounting for variances lets say 200w per panel x 10 panels x 6 hours. 12kwh of power per day. divide by 24…500w continuous power (tapping off the batteries at night) is the budget. I am afraid there are no easy solutions for the fridge. 335 wh, as above, /365= .917 kw. this is double my alowables with ten cells (conservatively). I would need another five cells to run this load and keep the lights on comfortably. I will talk to my boss tomorrow and ave him explain the finer points of solar refrigeration. That is what he started this company with.

I am so glad you commented. Thank you. We will ease your concerns in a minute. Your fridge will consume 335 kilowatt hours per year divided by 365 days equals .917 kilowatt hours (917 watt hours) per day. Now we need to divide that by 24 to figure out out the average load per hour which in your case is only 38 watts (.038 kW). Usually a fridge will run about a third of the time or 8 hours per day on average. So the maximum load your fridge will draw is 115 watts (917 watt hours divided by 8 hours = 115 watts).

To sum it up:
1. Your refrigerator will consume about .917 kWhs per day or use 38 watts on average.
2. Your refrigerator will be operating about 1/3 of the time or 8 hours per day.
3. .917 kilowatt hours divided by 8 hours of operating time = 115 watts while in operation.
4. You will need an inverter large enough to start your fridges compressor which is generally about 3 to 6 times the operating wattage. This is called a surge and your inverter must be rated to surge at somewhere between 350 to 700 watts. A 1000 watt sine wave inverter will work perfectly if that is the only load on your system.

If you are making 12 kWh (500-600 watts on average) per day you are looking really good. No need to worry. You are doing a great job. Keep up the great work. If you want to talk about it don’t hesitate to call me at 506-300-0600. By the way we get on average 1 hour of sun in January and 4.5 in the best of the summer months. I am so jealous. I’ve been to the San Fransisco Bay Area up to Napa and Arcata a few times but never got below Santa Cruz. If I ever get to LA I will make plans to visit Polar Power Inc. Take Care…Jody

Hi Jody: I’m confused about this calculation: “So the maximum load your fridge will draw is 115 watts (917 watt hours divided by 8)”. Wouldn’t the calculation you want to use be 38 watts (average load per hour) multiplied by 8? Which is 307 watts maximum load per day? Please advise!
Doing our own calculations here for a houseboat in NY, very happy to have come across your blog.

Thanks for contributing. It takes all of us to figure this stuff out. There is so little accurate info available.

So the first thing we will clear up is the fridge we are talking about consumes 917 watt hours (.917 kilowatt hours a.k.a. kWhs) per day.

If we divided that consumption by 24 hours in a day we would get an average load of 38.2 watts but a fridge operates approximately 8 hours per day depending on ambient temperature, how full it is, how many times the door is opened and how clean the cooling unit (condenser) is.

As a fridge usually operates about 8 hours per day (or a third of the time) the actual load while the refrigerator is running is 115 watts.
This is calculated by the following:

917 WATT HOURS / 8 HOURS = 114.6 WATTS.

The fridge only runs about 8 hours per day but it must consume a whole day’s worth of electricity in that 8 hours.

We can check our answer by working the formula backwards.

Let’s pretend we have a fridge that consumes 917 watt hours per day (as in our example).
The fridge only operates 8 hours per day.
This fridge uses 114.5 watts (or 115) while operating.

A standard 18 cuft fridge would use about 1000 watt hours or kWhs per day. If you tell me where you are located I will let you know how much solar and how many batteries. Need at least a 2000 watt continuous duty (2500 watt surge) inverter like a Magnum Energy or Outback Power. Must be sine wave not modified sine wave or modified square wave. It really depends on how many sun hours you get per day. Thanks for commenting..Jody

I’m very pleased to find this website. I need to to thank you for this fantastic read!!
I am going off the grid and am trying to pick the best appliances,
I definitely enjoyed every bit of your article and i also have you
bookmarked to see new articles in your site. Please keep writing.

Very helpful information. I stumbled upon your website researching energy efficient refrigerators. I don’t live off grid, unfortunately, but u wish to be as energy efficient as I can. It was useful to lnow the downsides to buying a SunFrost fridge, such as difficultly repairing, and transport costs. Why won’t more stores sell energy efficient fridges???
Thank you, Dee Ceop

Thank you for your comment.The Sunfrost really are beautiful machines. I have been an acquaintance of the owner of Sunfrost for years now. They are made in Arcata, California and made well. If I lived there I would be using one. But living on the other coast it just doesn’t make sense for me.

The typical refrigerator made today is certainly more efficient than it was twenty years ago but it could be much better. I think the reason high efficiency fridges are not sold everywhere is the fact that electricity is cheap. If the average consumer sees a more efficient fridge that costs $300 or $400 more they will buy the cheaper model as it might take years to recoup the extra money spent. The off grid homeowner will spend the extra money as they will spend much less on their solar system for every kilowatt hour they save. If electricity was more expensive I think we would see a movement toward more efficient appliances.

The other reason is there are large margins on cheap junky refrigerators made in China. Companies like Walmart want to make huge margins and they couldn’t if they sold quality. Thanks again and keep up your good work…Jody

Regarding Refrigerators, ~ 18-20 cft., the minimum consumption that the rating services show at this time is 311 Kwhs/yr. But, even at that low consumption, ALL have auto defrost. It could be that at this size have them built in.
Have you seen systems where the auto defrost can be shut off?

Hi. Thanks for the kind words. I haven’t had much time lately to write any articles as we are in the middle of winter and it has been a cold one. 311 kWhs per year is very good for a 18-20 cubic foot fridge. I have not seen a fridge without auto defrost for probably about ten years. They all seem to have it. I have not seen any that have a shut off either. You can disable it if you get a good wiring diagram and find the computer that operates it. Auto defrost is a nuisance for many reasons. They always seem to defrost at the worst times like a 20 below zero night when your batteries are low from a cloudy few days. Mine has never defrosted on a sunny day when I am dumping power anyway. The other issue is the auto defrost computer will get messed up if you are making anything less than a perfect 60 hertz sine wave. Having an AC generator that either outputs too much voltage and frequency or too low will almost always make your fridge defrost more than it is supposed to and a modified sine wave inverter will completely mess up the auto defrost. The only fridge I can recommend without auto defrost is the Sunfrost but they are very expensive and hard to get repaired if necessary. Sorry I am not much help…Jody

Thanks, I confirmed using the data available on Energy Star ( http://www.energystar.gov/certified-products/detail/refrigerators ) that they all mass produced refrigerators have that function.
I appreciate the less-than-sine challenges that these and other electronics have off grid. Luckily, more pure Sine wave inverters are becoming available (along with cheaper panels and CCs) .
No promises on when, but I plan to learn how to convert the defrost to manual, and test it on a modern refrigerator. when I do, I’ll post a link.
Thanks for setting up this site!

Thank you so much for clearing up my confusion about off grid refrigeration. I have been planning on building an off the grid home for about 7 years but have always worried about keeping my food cool. I am so glad I did not buy a propane fridge. Is there a particular brand or type of fridge you would recommend? I live outside of Dallas, TX. Any help would be appreciated….

I just read through the entire article about purchasing a fridge. It was great to see there are ways to have a refrigerator in an off the grid home. I just assumed it was not possible. I will visit your blog regularly for updates.

A is the best of your four, for your question, but since idnaviduil wind and solar power generate power to a battery, which is the direct source of power to your house, you can store up enough power to maintain your electrical usage, through the winter, power outages, and you can sell some access back to the Community Power Company. If enough households demand an idnaviduil windmill and solar panel, the initial costs will come down to reasonable expense!!

OK. Well let’s not plan for a month but a week might be reasonable. Nothing wrong with starting with the 12 volt Walmart marine batteries. They won’t last like a 6 volt but we all have a budget and work with what we have. Most of us anyway. We have been due for a new battery bank for a year but we don’t have the money. So we struggle along with our worn out batteries.

Your fridge uses 1107 watt hours per day on average. Multiply that by seven to get the consumption for a week or 7749 watt hours (or 7.749 kWh)
Each of your batteries will store 1436 watt hours (114 amp hours x 12 volts).

To be completely independent and only use 50 % of the battery bank’s capacity, you would need ten units. Ten units would provide a battery bank of 14360 watt hours (or 14.360 kWh) which is double what the fridge would use over a 7 day period.

That amount of batteries is ideal. However you do have a large solar array that will be adding electrons back to your battery through out the week.

And I don’t know what you budget is. You could try six or even 8 batteries and see how it works. If all is well then go with it. If you find the batteries are always struggling to keep up with the fridge you can always but more as long as it is within 3 or 4 months. It is not good to mix batteries with different ages but 3 or 4 months will be no problem. Hope that helps…Jody

Thank u so so much
Ur the first person willing to tell me some sort of info
That’s what I was thinking
10-12
And I was thinking of a timer
To shut off fridge like maybe 3-5 hours at night
Keep jugs of frozen water in freezer
And some jugs of cold water in fridge
That way food is not ruined
Thank u
Is that a dumb idea?

You are so welcome. You could use a timer to keep the fridge run time lower at night. You could also use ice and water jugs but the amount of electricity saved will be nothing. Fridges run about 8 hours per day by themselves as they turn on and off according to the thermostats in the fridge and freezer. If you have 10-12 batteries you will be fine just letting things operate normally. Using ice jugs and such just saves power at night only to consume that power in the day to re-freeeze (recharge) the ice jugs. If you had an undersized battery bank you could theoretically use the ice jugs as a battery. They would store cold while the sun is shining and release it when the sun is not shining at night. If you have the 10-12 batteries things will work fine as is. Keep up the good work…Jody

Hi. You could definitely bring them home and trickle charge for the winter. You could also leave them in your cottage connected to the charge controller as usual and they would be happy there too.

A common misunderstanding is cold and how it affects batteries. Cold decreases the amount of storage capacity in the battery bank or reduces the amps hours while the battery bank is cold. You have noticed this in your car or truck if you live in a cold area. However, the colder your batteries are, the longer they last in months or years. Hot batteries degrade faster than cold batteries. Batteries will only freeze if they are dead. Charged batteries cannot freeze. A dead battery will have water separated from the electrolyte and the water can freeze. A charged battery will force the water to mix with the electrolyte making it impossible to freeze.

The only downside to leaving your batteries at the cottage all winter (besides theft) is if the solar panels stay covered in snow allowing your batteries to go dead. If you know the snow will not always be covering the solar panels, they will be better off connected to the solar as they will receive bulk, absorption and float charging instead of just float. Just disconnect any load like the inverter and everything will work fine. Plus you will get more time out of your battery bank. Keep up the great work. Jody